MOLECULAR-DYNAMICS SIMULATIONS OF FREE-ENERGY AND CONFORMATIONAL TRANSITION RATES OF CALIX[4]ARENE IN CHLOROFORM

In a previous article we introduced a reaction coordinate based on the unstable normal mode at the saddle point of the potential energy surf ace. We here calculate the free-energy distribution along this coordin ate for the isomerization of calix[4]arene in vacuo and in chloroform using umbrella sampling, with one umbrella covering the entire range o f the reaction coordinate. An excellent first guess at this umbrella i s obtained by performing a normal-mode analysis at various points alon g the reaction path. The isomerization rate constant of this reaction is determined using the reactive flux method and is found to be in goo d agreement with experimental data. The rate was found to be independe nt of the location of the transition state, as it should be. (C) 1997 American Institute of Physics.